Semiconductor nanocrystals or quantum dots are gaining interest as fluorescent tags for biological molecules due to their large quantum yield and photostability. Quantum dots are semiconductor crystallites 2 nm — 10 nm in diameter that contain approximately 500-1000 atoms of materials as cadmium and selenide. Quantum dots fluoresce with a broad absorption spectrum and a narrow emission spectrum. The larger the quantum dot the longer wavelength emitted. The broad absorption spectrum allows many different quantum dots to be excited with one excitation source. The emission spectra for each dot is typically very narrow, on the order of 30 nanometers, which permits spectral resolution of adjacent dots.

In order to employ quantum dots as biological tags, the nanocrystal must be water soluble and capable of being conjugated to the biological molecule of interest. To accomplish this, much effort has been dedicated to functionalizing the nanocrystal surface with water-soluble, reactive chemical moieties. To employ quantum dots in biological assays, the optical properties of functionalized quantum dots must be understood. One approach presented here, employs single molecule confocal microscopy to probe the fluorescent properties of functionalized quantum dots at the single particle level. Others have shown that unfunctionalized or bare quantum dots demonstrate fluorescence intermittency or blinking on the millisecond timescale. Carboxylated, amine activated, and bare quantum dots will be probed in an effort to understand the effect of the novel coatings on the optical properties.

Jeffrey R. Krogmeier

Physics Laboratory

Building 221 / B206

Mail Stop 8441

Telephone: (301) 975-2395

Fax: (301) 869-5700

E-mail: jkrog@nist.gov

Non-member